Canada’s Athabasca oil sands are big business. Around half of the nation’s oil production – nearly two million barrels per day – is extracted in Alberta. Ever since oil extraction began here in 1967, there has been controversy over the levels of pollution it causes. Now a study reveals the mining has had negligible impact on metal pollution in the Athabasca River 200 km downstream.
In recent decades there’s been concern extraction of oil from these sands is polluting the Athabasca River with metals and other contaminants. The problem is no-one knows what contaminant levels were like before mining began, so it’s hard to gauge the effect of the extraction.
With this in mind, Roland Hall from the University of Waterloo and colleagues measured metal concentrations in pre-industrial floodplain deposits and compared them with recently deposited river sediments.
In order to compare the floodplain deposits with the recent river sediments, Hall and colleagues normalised all the metal concentrations to lithium – a naturally-occurring metal that is not affected by human activities and so can be used to account for changes in contaminant concentrations due to variations in sediment grain size.
Of the 135 metal analyses, only three were at increased levels in recent river sediments, compared to the pre-industrial floodplain sediments. These were copper in 2010 and 2011, and chromium in 2013.
“For the other 132 river-bottom sediment measurements of various metals, including vanadium and other priority pollutants (Be, Cd, Pb, Ni, Zn, and most Cu and Cr samples), they all are at levels that correspond with natural baseline concentrations,” said Hall, whose findings are published in Environmental Research Letters (ERL).
This indicates the oil sands development has not increased metal pollution in downstream sediments in the Athabasca River. Instead the results suggest that the metals in the Athabasca River sediments are overwhelmingly supplied by natural sources. “They were likely derived from riverbank erosion, a natural process of metal delivery to downstream locations that has been taking place for thousands of years,” said Hall.
(Full comment by Kate Ravilious found at Environmental Research Web)